1. Field of the Invention
The present invention relates to a routing system for controlling communications paths in a communications network, and, particularly, to a variance type routing system provided at each of a plurality of nodes in a communications network. More particularly, this invention relates to a routing system which efficiently execute routing even in a large-scale communications network.
2. Description of the Related Art
A communications network comprises a plurality of nodes connected by communications lines with one or more user terminals connected at each node. To communicate between any two stations or user terminals, a communications path is established via one or more nodes as relays. Normally, a communications path between any two stations is established between two nodes to which those stations are connected, and a plurality of communications paths are thus present between such two nodes. Selecting one of those communications paths is called "routing."
Generally, routing should satisfy various conditions given below.
(a) Shuttling between two stations, and looping back via a plurality of nodes should not occur.
(b) Process and control for selecting a communications path should be simple.
(c) The communications lines should be used at high efficiency.
(d) No equipments should be left invalid.
(e) Design and management of the communications network should not be complex.
(f) The load of the communications network should be minimized.
To execute routing using communications lines at high efficiency under the condition (c), it is necessary to collect status information Q, such as the load of an output link, and communication process information P like information about the traffic and subjective transmission quality, for each link request at all the nodes constituting the communications network.
The communication process information P about the traffic and subjective transmission quality can be sent from a user terminal.
But, collecting the status information Q of all the nodes burdens an excess load on the communications network and/or results in an unnecessarily longer communication process. It is not therefore easy to collect the status information Q of all the nodes. This shortcoming becomes more significant particularly as communication demands high speed and the communications network becomes larger.